1. Field of the Invention
The present invention pertains to tension members such as wire or fiber rope which are used to transmit a force from one object to another or for carrying a load of some type. More specifically, the present invention pertains to multiple leg rope assemblies and fittings used therewith.
1. Description of the Prior Art
Typically, rope assemblies of the single leg type are utilized for a number of purposes in which a load or force is transmitted from one object to another. Such rope assemblies are used to lift loads by winches, cranes and the like, for towing land and water vehicles, for suspending bridge elements, etc. Marine operations utilize many rope assemblies in towing, anchoring, lifting, etc. In the past, these tension members were typically natural fiber ropes, wire ropes or chain. With improvements in synthetic fibers, recent years have seen development of high performance synthetic fiber ropes for tension members. In fact, synthetic fiber ropes are now made which have approximately the same strength as wire rope of the same diameter. Furthermore, synthetic fiber ropes are considerably lighter, corrosion resistant, more resilient and easier to handle. However, ropes or tension members of any kind usually require some sort of termination fitting for attachment to other rope assemblies, anchors, fittings, etc. Most of the termination fittings or other fittings for rope assemblies have been developed for wire rope or chain. These have been found unsuitable for many applications of fiber rope.
At the present time, there are a very small number of rope manufacturers that can produce synthetic fiber ropes of strength over six hundred thousand (600,000) pounds. In addition, such ropes may not be economically produced and are difficult to terminate. For this reason, it may be desirable to use multiple leg rope assemblies so that several smaller ropes in parallel may be utilized. The smaller size ropes are produced by many more manufacturers at a more reasonable cost. These multiple leg rope assemblies provide as much strength and weigh no more than the larger, more expensive and cumbersome single leg ropes.
At the present, there are available rope assemblies of synthetic fiber with great strength. However, because of their large size, the end fittings by which these rope assemblies are anchored or connected to other fittings or loads are very large, heavy and cumbersome. In addition, these end fittings cannot be easily disconnected while under tension and frequently are not removable without cutting the rope. Furthermore, these end fittings, when required to pass over or be wound onto curved surfaces, such as a winch or drum or roller, create a number of problems. Most importantly, when multiple layers of rope are wound onto a winch or drum so that the rope is wound over end fittings, the bulky underlaying end fittings require considerable volume and often cause damage to the rope. Furthermore, rigid terminations cause severe bending of the rope and terminations.
A typical termination for a rope assembly requires the fabrication of an eye or loop at the end of the rope. These eyes are often protected by metal thimbles which are placed inside the eye to act as a load bearing surface and to protect the rope. Such thimbles are large and heavy and act as an impediment to effective utilization of the rope. U.S. Pat. Nos. 2,426,538 and 2,495,951 illustrate sling and end fittings of one type in which a clevis is formed by splitting a single, large rope structure into two parts in order to form a clevis. Although the clevis is produced, the benefits of using a multiple leg assembly of smaller ropes is not obtained. Furthermore, this type of rigidly fixed clevis is not easily disconnected under tension and requires extremely close manufacturing tolerances complicated by the fact that the strands are on top of one another and some strands must travel a longer path over the fitting than others.
In many marine applications, it is desirable that rope assemblies have the ability to float or to be bouyant in water. Chains, wire rope and most higher performance fiber ropes do not float. When flotation is required, this is traditionally done by placing flotation sleeves on the rope. Flotation sleeves are relatively expensive, difficult to apply, vulnerable to damage and usually make the rope assembly difficult to handle and service. U.S. Pat. No. 4,593,599 discloses a single leg rope assembly made to float by wrapping buoyant material around the rope and covering it. A strong cover is necessary to hold the buoyant material in place.
Thus, it can be seen that the advent of high performance synthetic fiber rope has resulted in rope assemblies of improved characteristics. However, a number of problems are associated with such rope assemblies, particularly in the provision of termination fittings and other fittings for use therewith. Further improvements and developments in the utilization of fiber ropes are needed to obtain the greatest use thereof.